Issue 49

A. Pola et alii, Frattura ed Integrità Strutturale, 49 (2019) 775-790; DOI: 10.3221/IGF-ESIS.49.69

Si

Mg

Cu

Fe

Mn

Ni

Al

Zn

Pb

Sn

Ti

AlSi10Mg

9-11 0.2-0.45 <0.05 <0.55 <0.45

0.05

<0.10 <0.05 <0.10 <0.15 Balance

Table 1 : Nominal chemical composition (wt. %) of the commercial EOS Aluminium AlSi10Mg powder. In Fig. 1, the geometry of the specimens used for tensile (Fig.1a) and fatigue (Fig.1b) tests is shown. After manufacturing, the samples were sand-blasted by using the B120 Microblast Ceramic Beads of Saint-Gobain Zirpro at about 10 cm from the nozzle and for an exposure time of 2 min at 5 bar. The sand particles had a size distribution in the range of 63-125 µm. Their chemical composition, performed by X-ray fluorescence on melting sample by the producer, is reported in Tab. 2. The samples roughness (R a ) was measured before and after sand-blasting by a stylus profilometer (Tribotechnique) with a tip radius of 5 µm and an applied load of 1 mN.

Figure 1 : Specimen geometry for (a) tensile test and (b) fatigue test samples and (c) produced specimens

Min %

Max %

ZrO 2 SiO 2

60 28

70 33

Al 2 10 Table 2 : Nominal chemical analysis (wt. %) of the particles used for sand-blasting. O 3 0

A preliminary microstructural analysis was performed by optical (Leica DMI 5000M) and scanning electron (LEO EVO 40) microscope. To this aim, the samples were cut perpendicularly to the fabrication direction, polished up to mirror finishing and etched with Keller’s reagent (1% HF, 1.5% HCl, 2.5% HNO 3 and 95% H 2 O), applied for 30 s according to ASTM E407 standard [48]. A detailed defect analysis was carried out on four specimens to characterize the distribution of porosity. To this aim, a cylindrical specimen, with a length of 10 ± 2 mm, was obtained from the gage length of four sand-blasted AlSi10Mg fatigue samples performing a double cut, perpendicularly to the axis of the sample, with a Struers Labotom machine. The specimen was ultrasonically cleaned in ethanol, dried and inserted in a cold mounting resin. After the solidification of the resin, the mounted specimen was grinded and polished up to mirror finishing, starting from P220 grinding paper till to a velvet cloth with Struers colloidal silica suspension. Finally, the specimen was ultrasonically cleaned in ethanol and dried with warm air. The optical analysis was performed by means of Leica DMI 5000 optical microscope mapping the whole polished section of the specimens with 120 ± 5 images at a magnification of 50x. The entire section was reconstructed with the support of the Leica Application Suite v4.8 software. The whole sections were processed using a custom software for defects analysis coded within NI Labview environment that evolved from previous approaches used for marker tracking [49] and crack length tracking [50] during various experimental tests. This new optical measurement code allows the processing of single or multiple images and provides a text output file containing all the data of the most significant features of each defect identified in the image(s) such as: position, bounding box, orientation, elongation, area, maximum Feret diameter, and many others. High resolutions images (over 100 Mpx) and high numbers of defects per image can be handled with ease.

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